The cell potential for the given cell at 298 K

Pt| H₂ (g, 1 bar) | H⁺ (aq) || Cu²⁺ (aq) | Cu(s)

is 0.31 V. The pH of the acidic solution is found to be 3, whereas the concentration of Cu²⁺ is 10^$-$x M. The value of x is ___________.

(Given : $E_{C{u^{2 + }}/Cu}^\Theta$ = 0.34 V and ${{2.303\,RT} \over F}$ = 0.06 V)